Apr 22, 2013 7:44 AM

This has the scalloping on the hind wing and the forewing costa is very rounded. Why should this not be identified as Gonepteryx farinosa (Powdered Brimstone) other than the geographic location? My guide shows that the forewing costas of farinosa and rhami having concave sections in the forewing costa and the difference being the rounding near the root of the wing, farinosa being generously rounded as in this specimen. Rhami does not have scalloping. So is this really possible?

Geographic location is very important. This specimen was found way out of G. farinosa's natural range, so by this alone I would guess it's not that species. It also looks more like the Brimstone illustrated in my book than a Powdered Brimstone: underwing green rather than yellow, well developed 'tail' on hindwing. I think it's G. rhamni.

I worry about the geographic argument as species are often spread out of their natural range by inadvertent human actions so I am more interested in objective arguments based on the appearance of the specimen.

I am interested in your argument based on colour. I have Collins and the drawings in that book of farinosa are very definitely yellow. But I also have Haahtela et. al. which has no drawings and only photographs. The photographs in that book show a very slightly yellow green and in all other resepcts look like the photograph I uploaded. I don't know if you have access to that book - it was purchased in the NHM bookshop! Does this mean the authors may have incorrectly identified those photographs? I'm beginning to think they may. Their description of rhamni includes the forewing "apical hook well developed" while for farinosa "a weak apical hook" but in the photographs (on facing pages!) they look identical.

I strongly suspect that my specimen is rhamni as it doesn't even have a slight yellow tinge but if you have an opportunity to look at Haatela I'd be most interested in your observations on their photos.

I await your further research. While on this subject, and just to add more grist to the mill, I revisited an old enquiry of mine and I was reminded of another feature of farinosa - the antennal club is described as "white or pink above" (in Haatela et al though not in Collins). Looking closely at the image I uploaded you can see that the club closest to the camera (the one on the right) does have a light coloured tip, much as in the photo in Haahtela. (The far antenna is at the wrong angle to see clearly but there is a suggestion of a light tip.) I can see no mention of a light coloured tip in rhamni.

First, I re-processed my original photo because the scalloping on the hind wing was somewhat obscured by shadow so I've tried to get a more balanced photo. Second, I've photographed the relevant pages (fortunately consecutive) in Haahtela. Both photos are attached so you get them in full resolution.

What I notice are:

1) My specimen has scalloping as shown in the Haahtela photo.

2) My specimen has an antenna (the one on the right which I think is the one closest to the camera) that resembles the photo in Haahtela.

3) My specimen has a slight concavity where V1 meets the costa on the forewing. I can't make up my mind if there is a concavity in the Haahtela photo but if there is it is less than in my specimen.

4) The Haahtela photo is a slightly yellow green, nothing like the yellow shown in Collins, but more yellow than my specimen. On the othe hand, my specimen is more yellow than the Haahtela photo of rahmni.

It's quite confusing. My specimen is more like farinosa on two counts and more like rahmni on one count and indeterminate on the fourth. I seriously wonder if the Haahtela photo is correct. On the other hand, if my specimen is rahmni then the scalloping can no longer be considered a defining characteristic of farinosa.

I have a photo guide Butterflies of Europe by Trstan Lafranchis which shows pictures of your butterfly. The farinosa has definite white tips on the upper surface of the antennae which it says is a defining character compared with brown tips on rahmni.

This might help but I am not surprised that the identification is difficult.

Difficult! It's driving me mad! If you've looked at the extract from my book which I attached to my last post you can see clearly that the author lists 4 defining characteristics for farinosa:

1) Fw costa rounded. (Not how I would describe the example in his photo - in fact checking it out enlarged there is a definite albeit small concavity at V1)

2) Hw margin scalloped (pretty similar to my photo and to a photo posted some time ago which was said to be rahmni because of the concave forewing costa)

3) A weak apical hook! (I've compared his photos of rahmni and farinosa and I just don't get this as I can't see what the difference is supposed to be)

4) Antennal club white or pink above.

This last is probably the most important but most difficult to establish. When I look at the butterfly I photographed the antenna nearest the camera appears light pink on top with a dark ring and a yellow tip while the one further away looks white - but I'm convinced that latter is mainly due to reflected sunlight. How much of the closer antenna's pink top is due to reflected sunlight who can tell? In the photo from the book, the antenna furthest from the camera appears white on top while the one closest appears pink, with a black ring and a pink tip. The photo of the male rahmi seems to have a slightly pale upper surface (where the light catches it, no doubt) but it does not have a light tip. The photo of the female rahmi antennae is not clear but one may have a white tip.

Anyway, I'm not clear, when you say "shows pictures of your butterfly" do you think your LaFranchis book would classify my butterfly as farinosa or rahmni?

Sorry to reply so late, and thanks for posting the images in the Haahtela book. I don't have it here in the AMC, but I do have the Lafranchis book. As far as I understand, the best character is the anterior margin of the forewing. In rhamni the forewing costa are slightly concave, while in farinosa they are regularly rounded. So that line is usually straight or rounded in farinosa, and bent inwards in rhamni. The photos in the Haahtela book seem to show this pattern.

The other character is the antennal club, supposedly white(ish?) in farinosa. If you google images of farinosa, you will find some with clear white antennal clubs. One of the photos in the Lafranchis book (page 60) looks like this, but I noticed that rhamni seems to have light-coloured antennal tips depending on how the light reflects on them.

I have asked a Museum butterfly expert for help, and he has found another expert who will take a look at your photo, but he's not in for a couple of weeks and he will reply when he returns.

The forewing costa is an interesting issue. Re farinosa I've checked the line on the image in Haahtela and it has a very slight concavity at V1. Admittedly, it is far less than in the image I took.

The only similar image in the link you supplied for farinosa in your second message (the top image) also has a slight concavity and there is a comment underneath stating,

"A correspondent has correctly identified this as G. rhamni, not farinosa. Note the concave costa - this should be straight or convex in farinosa."

Which takes me back to one of my original questions - did Haahtela accidentally include an image of rahmni and pass it off as farinosa? If that is the case no wonder it is so difficult to tell these apart.

The specimen on the right of these two has a small concavity at V1. It may be incorrectly identified but it is a photo of a mounted specimen rather than a fleeting glimpse of a butterfly in the wild so I presume the chances of misidentification are lower. There is another:

I guess the issue for me is to understand what are the real defining characteristics that differentiate between these two species. I am a scientist by training so I consider it essential that there must be one or more characteristic that will differentiate between two species otherwise this is all smoke and mirrors. With digital photos it is easy to see if a line is straight, convex or concave. It is more difficult to see if antennae are white/pink because reflected sunlight can alter the appearance of the colour. Scalloping, I suspect, cannot be used to differentiate. I've measured the 'degree of scalloping' shown in the 2nd specimen photographed at Vaud, Switzerland, (http://www.eurobutterflies.com/species_pages/rhamni.htm) and compared it with the bottom image of the NHM specimen of farinosa included (http://www.eurobutterflies.com/species_pages/farinosa.htm). They are identical within the limits of my ability to measure on the small images.

I will await the comments of your expert whose attention I hope you will direct to the links I've supplied above.

I would have to say that this is G. rhamni, based on the concave forewing costa. The character of the scalloped margin to the hindwing assumes that the wing is flat and is viewed at 90 degrees; in the photo the wings are clearly at an angle, i.e. so any distortion to the wing might produce this scalloped effect. I am doubtful of the value of the apical hook character, but its use would also depend on the wings being flat. I would also suggest that Interpretation of wing colour and the possible pale tips to the antennae from a single photo is not wholly reliable. The geographical aspect is significant, given the known range of G. farinosa; if the presence of this species in Spain was suspected, it would require confirmation by examination of specimens.

I am happy to accept that this is rahmni. But the wider question seems to me to be still open - what are teh characteristics that determine if a specimen is farinosa? I am intrigued by the commen of your expert about distortion of the wing producing a scalloped effect. I would have imagined that two wings together would naturally lie flat and that viewing off the perpndicular could then only reduce the scalloped appearance. It seems we are left with the white on the antennae being the only reliable method of identification in the field, provided it can be clearly seen not to be an effect of reflected light.